Hi Dave. I'm having a problem similar to the one I reported & we solved around 4/6/16. I've started using Mountain to prevent some drives from unmounting, including the HD source drive. I'm still running Yosemite. My nightly backup does an Update on 2 drives - HD & SSD.

Suddenly, HD is not being backed up, without any error messages, anything relevant I can find in Console logs or SuperDuper logs. I've upgraded Superduper to 3.0. I've deleted & re-entered the Schedule. I've tried doing a manual backup - it works!